For the design case of 3 × 1W high brightness white LED light source, three 1W LED light sources are connected in series, and their working current can be designed as 300 ~ 350mA. The inductance of l should be 68uh ~ 100uh, Q value is greater than 50, and saturation current is greater than 800mA.
Pt4115 is designed with the best working frequency below 1MHz, and its working frequency will be affected if the inductance is large or small. In this scheme, the inductance is designed above 68uh, so that the working frequency of the system can be controlled below 1MHz. Due to the limitation of response speed of pt4115 internal current detection circuit, the normal detection of internal current is affected, and the on / off control of internal switch cannot be realized better. In addition, high frequency will bring large switching loss, which makes the chip run at a high junction temperature, increasing the electrical stress, which is not conducive to stable operation. Too small inductance will also cause the SW end of pt4115 to burn out without output.
The smaller the DCR of the inductor, the higher the efficiency. Epc13 manganese zinc 4000 core is recommended.
If the saturation current of the inductor and the current of the D5 Schottky diode are smaller, the continuous current of the whole circuit will be insufficient, and the LED light source will produce the flash visible to the human eye. When the saturation current of inductor and the current of Schottky diode are properly increased, the continuous current of the whole circuit can be increased, and the flash generated thereby can be eliminated.